The present invention relates to a method of reducing the clogging of nozzles and slits and diminishing the formation of deposits in a spin bath system in a process of making viscose filamentary and film materials by using an amphoteric surfactant.
When regenerating cellulose material in an acidic spin bath containing zinc sulphate, clogging disturbancies are frequent. The origins of the clogging material are different. One and the most important source are solid by-products, i.e., elementary sulphur and zinc sulphide, which are formed when the dissolved xanthogenated celluloses are regenerated to cellulose and carbon disulphide. Other examples of by-products are hemicelluloses and resins derived from the cellulosic raw material itself and transfered to the spin bath where they cause deposits.
One method of reducing these disadvantages is to add cationic surface active compounds to the spinning baths. Thus, in Japanese Patent No. 48006409 it is suggested to add N,Nxe2x80x2-polyoxyethylene-N-long chain-alkyl alkylene-diamines and N,Nxe2x80x2,Nxe2x80x3-polyoxyethylene-N-long chain-alkyl alkylene-triamines into the spin bath as dispersants for sulphur particles which cause blockages in spinning nozzles. The long-chain alkyl group contains from 10 to 20 carbon atoms. The number of oxyethylene groups are from 1 to 8 for each substitution position and their sum is from 2 to 10. However, these additives have a rather limited ability to disperse sulphur, especially when the amount thereof is high.
In Japanese Patent Application No. 54101916 it is suggested to add polyoxyethylene alkyl mono- and diamide polyalkylene polyamines to further reduce the clogging of nozzles. Examples of the used polyalkylene polyamines are triethylene tetramine and tetraethylene pentamine. The number of carbons in the fatty acids used for preparing the compounds is preferably from 12 to 22, while the number of ethylene oxide groups in the molecule is from 6 to 12. Although these polyamines have a good dispersing effect they have a serious drawback since they are not stable in hot acid solutions and are hydrolyzed at high temperature in the spin bath. Consequently, after some time their effect is essentially reduced.
The degradation of the additive can be compensated by addition of higher dosages of the additives. However, in practice the resulting products of the hydrolysis, i.e., the fatty acids produced especially during reconditioning of the spin bath enhances the clogging. Together with elementary sulphur and/or zinc sulphide and resins they form black particles, which are very difficult to disperse.
It has now been found that not only the disturbancies of clogging materials in the spin bath are essentially diminished but also the quality of the fibers formed in the spin bath is improved by using an amphoteric surfactant having the formula I
RNA (CnH2nNA)xxe2x88x921Axe2x80x83xe2x80x83(I)
where R represents a hydrogen or an aliphatic group with 1-24 carbon atoms, each A represents a hydrogen, an aliphatic group with 1-24 carbon atoms, or BOOCCmH2mxe2x80x94 groups, where m is a number from 1-3, B is hydrogen or a salt forming cation, n is a number from 2-3, x is 1-8, and the number of BOOCCmH2mxe2x80x94 groups are from 1 to x+2, with the provision that the total number of carbon atoms in the aliphatic groups is from 8 to 45, as a viscose spin bath additive.
The invention is a spin bath additive of an amphoteric surfactant having the formula I
RNA (CnH2nNA)xxe2x88x921Axe2x80x83xe2x80x83(I)
where R represents a hydrogen or an aliphatic group with 1-24 carbon atoms, each A represents a hydrogen, an aliphatic group with 1-24 carbon atoms, or BOOCCmH2mxe2x80x94 groups, where m is a number from 1-3, B is hydrogen or a salt forming cation, n is a number from 2-3, x is 1-8, and the number of BOOCCmH2mxe2x80x94 groups are from 1 to x+2, with the provision that the total number of carbon atoms in the aliphatic groups is from 8 to 45, as a viscose spin bath additive.
The amphoteric surfactant has an excellent anticlogging effect, since it is a good dispersant and prevents or reduces precipitation in the spin bath. In addition, it has low foaming and is very stable in comparison with the amide compounds disclosed in JP Patent Application No. 54101916. Since the additive keeps the openings in the spinneret free from clogging materials, the filaments and films formed collect fewer solid particles, whereby the discoloration is reduced and the fiber or film strength improved. The maintainance of the spin bath is also simplified, since the amphoteric surfactant is stable in ordinary working-up-processes of the spin bath and the spin bath solution can be recirculated after the removal of an excess of the by-products including sodium sulphate obtained in the spin bath. The amount of the amphoteric compound in the spin bath may be varied within wide limits, but is normally added in an amount of 0.5-5000 ppm, preferably from 2 to 1500 ppm, to a spin bath containing 5-15% by weight H2SO4, 15-30% by weight of Na2SO4 and 0-7% by weight of ZnSO4.
The amphoteric surfactant of formula I preferably contains one or two aliphatic groups, R and A, with a total of 8 to 40 carbon atoms, preferably from 10 to 36 carbon atoms. Preferably R is a hydrocarbon group with 8-24 carbon atoms, and most preferably 10-22 carbon atoms. B is normally a mono- or divalent, preferably a monovalent cation, m is preferably a number 1 or 2.
Most preferred amphoteric surfactants of the formula I are those having the formula
RNA (C3H6NA1)xxe2x88x921A1xe2x80x83xe2x80x83(II)
where R, A and x have the meaning mentioned in formula I and A1 is a hydrogen or a group BOOCCmH2m, where B and m have the meaning mentioned in formula I. These additives are easy to produce and have excellent dispersing ability. Normally at least 50% of all substituents A and A1 are the group BOOCCmH2mxe2x80x94. The amphoteric surfactants where m is 1 are preferred, since they exhibit low foaming. Low foaming is also supported by the presence of at least one R group with 14-22 carbon atoms. This is of benefit in the sequent treatment of the fiber and film material.
The present invention also relates to a process for regeneration of cellulose from a viscose solution, in which process the viscose solution is brought into contact with a spin bath containing from 0.5 to 5000 ppm of an amphoteric surfactant according to formula I. Preferably the amphoteric surfactant has the formula II. The spin bath normally has a temperature of from 40xc2x0 C. to 60xc2x0 C. and contains in addition to the amphoteric surfactant from 5 to 15% by weight of H2SO4, from 15 to 30% by weight of Na2SO4 and from 0-7% by weight of ZnSO4. The regenerated cellulose may have the form of fibers or films or any other conventional shape.